Milwaukee M18 battery powering my fishfinder

Never had luck with Nocqua batteries. I made the switch to a Milwaukee M18 12 ah battery with a 12v converter to power my Lowrance Elite FS 7. I use these batteries for work, so I have lots of them. So far so good.

I bought a couple of these for my makita battery’s and has worked well powering my fish finder as well as other good uses. Once I’m off the water, I use this power washer with the same makita battery to wash down gear before hitting the road.

Nice idea...

Curious,  I just got a Garmin that states power input of 12-20 volts.
The website tech section has a warning to not use I think they said " drill batteries " I'm going to look at that regulator,  but anyone else have input about it?
O.p.
Got a link/ info on the regulator?
How's it worked out?